Toward an improved structural model of the frog‐skin antimicrobial peptide esculentin‐1b(1‐18)

Abstract

Antimicrobial peptides (AMPs) are found in various classes of organisms as part of the innate immune system. Despite high sequence variability, they share common features such as net positive charge and an amphipathic fold when interacting with biologic membranes. Esculentin-1b is a 46-mer frog-skin peptide, which shows an outstanding antimicrobial activity. Experimental studies revealed that the N-terminal fragment encompassing the first 18 residues, Esc(1-18), is responsible for the antimicrobial activity of the whole peptide, with a negligible toxicity toward eukaryotic cells, thus representing an excellent candidate for future pharmaceutical applications. Similarly to most of the known AMPs, Esc(1-18) is expected to act by destroying/permeating the bacterial plasma-membrane but, to date, its 3D structure and the detailed mode of action remains unexplored. Before an in-depth investigation on peptide/membranes interactions could be undertaken, it is necessary to characterize peptide's folding propensity in solution, to understand what is intrinsically due to the peptide sequence, and what is actually driven by the membrane interaction. Circular dichroism and nuclear magnetic resonance spectroscopy were used to determine the structure adopted by the peptide, moving from water to increasing amounts of trifluoroethanol. The results showed that Esc(1-18) has a clear tendency to fold in a helical conformation as hydrophobicity of the environment increases, revealing an intriguing amphipathic structure. The helical folding is adopted only by the N-terminal portion of the peptide, while the rest is unstructured. The presence of a hydrophobic cluster of residues in the C-terminal portion suggests its possible membrane-anchoring role.

d-Amino acids incorporation in the frog skin-derived peptide esculentin-1a(1-21)NH2 is beneficial for its multiple functions

“…Similar results were found for the shorter analog, Esc-1b(1-18)NH 2 (Gly-Ile-Phe-Ser-Lys-Leu-AlaGly-Lys-Lys-Leu-Lys-Asn-Leu-Leu-Ile-Ser-Gly-NH 2 ) Manzo et al 2012), which is less active against gram-negative bacteria, e.g., P. aeruginosa, and differs from Esc(1-21) by a single amino acid at position 11, and lacks the 3 residues tail Leu-Lys-Gly-NH 2 at its carboxyl end.…”

The effect of glycine replacement with flexible ω-amino acids on the antimicrobial and haemolytic activity of an amphipathic cyclic heptapeptide

“…In order to do so, we introduced several flexible linkers in the structure of 1 and we monitored the effects of such substitutions on its antimicrobial and haemolytic activity. Many of the structural investigations aimed at characterizing membrane-active AMPs focus on the amphipathicity-driven, early stages of membrane association [26,32,[38][39][40]. This is presumably due to established spectroscopic and calorimetric methods being best suited for the investigation of these thermodynamic events [41].…”

“…Spectra were recorded in water with minimal organic solvent (acetonitrile) and in water with 50% trifluoroethanol (TFE), an established membrane-mimicking agent [30][31][32]. Due to their high absorbance in the UV range, electronic transitions of the naphthyl groups are responsible for the observable signals and, overall, the observed spectra are clearly reminiscent of previously reported peptides with multiple naphthyl groups [33,34].…”

Defending the fort: a role for defensin‐2 in limitingRickettsia montanensisinfection ofDermacentor variabilis

“…After the initial attraction and attachment, AMPs are theorized to assume their folded secondary structure (Matsuzaki, 1999; Marcellini et al , 2009; Rahman et al , 2009; Manzo et al , 2012). A transmembrane pore is thought to form through three mechanisms and appears to be peptide concentration-dependent.…”